(i) Technical Field
The present invention relates to a registration mark including a set of toner patterns that give information of toner-image formation positions of plural toner-image forming units, and relates to an image forming apparatus that adjusts the toner-image formation positions by using such a registration mark.
(ii) Related Art
There is known an image forming apparatus that obtains a color toner image by overlaying toner images of plural colors on each other. In many cases, such an image forming apparatus adjusts toner-image formation positions of the toner-image forming units that form toner images of respective colors in order to overlay the toner images with high accuracy. When the current toner-image formation positions are detected for the adjustment, a method using a registration mark including a set of toner patterns formed by the toner-image forming units of the respective colors is frequently employed. With this method, the toner-image formation positions are detected based on a signal acquired when an optical sensor that emits light and receives reflected light radiates the registration mark with light and receives reflected light.